Force in an internal combustion engine is typically produced by igniting fuel, using an ignition system, in a combustion chamber. The type of ignition system depends on the type of engine. For example, a diesel engine can be ignited using compression heating, while a petrol or gasoline engine can be ignited using a spark (e.g., from an igniter, or a spark plug).
Generally, to generate a spark to ignite a gasoline engine, ignition systems include a power source (e.g., a battery), a transformer (e.g., an ignition coil), a switch (e.g., to control a current in a primary coil of the transformer), and an igniter. Because a voltage across an inductor (or a coil) is proportionate to a change in current in the inductor (V(t)=di(t)/dt), an immediate change in current through a primary winding of the inductor can produce a high voltage. An ignition coil typically includes a primary coil and a secondary coil. Generally, the voltage on the secondary coil is proportionate to the voltage on the primary coil, amplified by a ratio of turns between the primary and secondary coils. In certain examples, the voltage on the secondary coil can approach 10-20 kilovolts, which, once generated, is impressed across a gap on the igniter. Once the voltage across the gap exceeds the dielectric constant of the air in the vicinity of the gap, a spark is produced across the gap, igniting fuel (e.g., a gasoline-air mixture) in the combustion chamber.
Over time, the switch has evolved from a mechanical switch (e.g., breaker points in a distributor), to a high voltage Darlington bipolar transistor either in the distributor or in a separate electronic control module, and now to an insulated gate bipolar transistor (IGBT) in an ignition coil proximate the spark plug.